Method for operating an electrohydraulic valve control system of an internal combustion engine, computer program, and control, and regulating unit for operating an internal combustion engine

ABSTRACT

An electrohydraulic valve control ( 10 ) of an internal combustion engine includes at least one actuator ( 24 ) that acts on a gas exchange valve ( 38 ). This actuator ( 24 ) in turn has at least one working chamber ( 30 ), which in order to switch the actuator ( 24 ) from a first position into a second position, is connected to a high-pressure hydraulic accumulator ( 16 ) and shut off from a low-pressure return ( 56 ). In order to switch the actuator ( 24 ) from the second position back into the first position, the working chamber ( 30 ) is connected to the low-pressure return ( 56 ) and shut off from the high-pressure hydraulic accumulator ( 16 ). The pressure in the high-pressure hydraulic accumulator ( 16 ) is kept constant or reduced in a simple manner by virtue of the working chamber ( 30 ) being connected to the high-pressure hydraulic accumulator ( 16 ) and the low-pressure return ( 56 ) at the same time.

PRIOR ART

[0001] The invention relates first of all to a method for operating an electrohydraulic valve control of an internal combustion engine, with at least one actuator that acts on a gas exchange valve and has at least one working chamber, which in order to switch the actuator from a first position into a second position, is connected to a high-pressure hydraulic accumulator and shut off from a low-pressure return, and in order to switch the actuator from the second position back into the first position, is connected to the low-pressure return and shut off from the high-pressure hydraulic accumulator.

[0002] A method of this kind is already known from the market. Electrohydraulic valve controls of internal combustion engines permit gas exchange valves to be triggered independent of the position of the crankshaft or camshaft. Among other things, they permit fuel savings and improvements to the emissions characteristics of an internal combustion engine to be achieved.

[0003] In an electrohydraulic valve control that is known from the market, the shaft of the gas exchange valve is connected to a hydraulic actuator. This actuator has two working chambers of different sizes on the two sides with the piston end faces. The small end face is continuously acted on by high pressure from a high-pressure hydraulic accumulator, which is in turn supplied by a hydraulic pump. The large end face of the piston is alternatively connected either likewise to the high-pressure hydraulic accumulator or to a low-pressure return. Depending on which of these it is connected to, a force resultant is produced, which opens or closes the gas exchange valve.

[0004] In the known method, there can be considerable variation in the quantity of hydraulic fluid, which flows out of the high-pressure hydraulic accumulator via the actuator, to the low-pressure return, and is used to switch the actuator. The fluid quantity that the hydraulic pump feeds into the high-pressure hydraulic accumulator can also vary, for example if the hydraulic pump is driven directly by the internal combustion engine and the delivery capacity of the hydraulic pump therefore depends on the engine speed.

[0005] In order to nevertheless be able to achieve a relatively constant pressure associated with the operating point in the high-pressure hydraulic accumulator, it has previously been necessary to provide a pressure relief valve or pressure control valve, for example, which drains hydraulic fluid from the high-pressure hydraulic accumulator when a certain pressure is exceeded. Another known method is to regulate the delivery quantity by means of the hydraulic pump. Dynamic pressure peaks in the high-pressure hydraulic accumulator can also be passively smoothed out by means of large volume of the high-pressure hydraulic accumulator.

[0006] The above-mentioned means for keeping the pressure constant in the high-pressure hydraulic accumulator, however, are relatively expensive and some react only sluggishly to pressure changes in the high-pressure hydraulic accumulator. Also, a large high-pressure hydraulic accumulator for smoothing out pressure peaks is disadvantageous because there is usually only a small amount of space available, e.g. in the engine compartment of motor vehicles. A pressure control valve has the same disadvantage.

[0007] The object of the current invention, therefore, is to modify a method of the type mentioned at the beginning so that the pressure in the high-pressure hydraulic accumulator can be kept constant in a simple manner.

[0008] This object is attained with a method of the type mentioned at the beginning in that the pressure in the high-pressure hydraulic accumulator is kept constant or reduced by the working chamber being connected to the high-pressure hydraulic accumulator and the low-pressure return at the same time.

[0009] Advantages of the Invention

[0010] The measures taken according to the invention permit the high-pressure hydraulic accumulator to be connected directly to the low-pressure return, without requiring additional components, e.g. a pressure control valve. In order to permit this, an operating state is expressly permitted in which the working chamber is connected to the high-pressure hydraulic accumulator and the low-pressure return of the electrohydraulic valve control at the same time. If it turns out, e.g. as determined by a sensor, that it is necessary to drain hydraulic fluid from the high-pressure hydraulic accumulator in order to be able to keep the pressure in it constant, then this can occur in a simple manner according to the invention in that the fluid flows through the working chamber to the low-pressure return.

[0011] Since the on-off valves usually used for this have a short reaction time and a highly dynamic switching behavior, then it is also possible to smooth out momentary fluctuations of the pressure in the high-pressure hydraulic accumulator. Therefore on the one hand, the method according to the invention permits the elimination of a pressure control valve. On the other hand, the high-pressure hydraulic accumulator can be smaller. This reduces costs in the manufacture of the electrohydraulic valve control and in addition, the electrohydraulic valve control takes up less space.

[0012] Advantageous modifications of the invention are disclosed in the dependent claims.

[0013] In a first modification, in order to stabilize or reduce the pressure in the high-pressure hydraulic accumulator, the working chamber of an actuator is connected to the high-pressure hydraulic accumulator and the low-pressure return simultaneously and its associated gas exchange valve is closed at the time. This modification of the method according to the invention is particularly suitable if an exertion of the full high pressure is used to trigger the actuator and open the gas exchange valve. In the closed neutral position of the gas exchange valve, therefore, the working chamber of the actuator usually contains a pressure, which is lower than the full high pressure of the high-pressure hydraulic accumulator.

[0014] When the high-pressure hydraulic accumulator is connected via the working chamber of the actuator to the low-pressure return, however, the working chamber of the actuator contains a pressure, which is lower than the full pressure in the high-pressure hydraulic accumulator. The closed neutral position of the gas exchange valve is consequently not influenced by this simultaneous connection of the working chamber to both the high-pressure hydraulic accumulator and the low-pressure return.

[0015] It is particularly preferable if, in order to stabilize or reduce the pressure in the high-pressure hydraulic accumulator, the working chamber of an actuator is connected to the high-pressure hydraulic accumulator and the low-pressure return simultaneously and its associated gas exchange valve cannot open at the time due to a high internal pressure in the cylinder. This effectively prevents an undesired opening of the gas exchange valve in an actuator that reacts “sensitively” to pressure fluctuations in the working chamber.

[0016] It is also possible for the working chamber of an actuator, which is to be moved from the first position into the second position, to be connected to the high-pressure hydraulic accumulator just before being shut off from the low-pressure return, and/or for the working chamber of an actuator, which is to be moved from the second position into the first position, to be connected to the low-pressure return just before being shut off from the high-pressure hydraulic accumulator.

[0017] In this case, a triggering of the actuator, which was intended anyway, is used to drain hydraulic fluid from the high-pressure hydraulic accumulator. This is made possible by shifting the time at which the working chamber is connected to the low-pressure return or to the high-pressure hydraulic accumulator. Consequently, there is an overlap of the times in which the working chamber is connected to the low-pressure return and to the high-pressure hydraulic accumulator. This makes it possible to integrate the stabilization or reduction of the pressure in the high-pressure hydraulic accumulator into the normal operation of an actuator.

[0018] In a particularly advantageous modification of the method according to the invention, the working chamber of an actuator is temporarily connected to the high-pressure hydraulic accumulator and the low-pressure return at the same time when the internal combustion engine is operated at a low speed. This modification takes into account the fact that at a low engine speed, a lower pressure in the high-pressure hydraulic accumulator is generally advantageous. Since such a deliberate pressure reduction in the high-pressure hydraulic accumulator was not previously possible, the triggering strategy of the actuator instead had to be changed at low engine speeds. This is no longer necessary with the modified method according to the invention.

[0019] Another modification includes the proposal that the pressure stabilization or pressure reduction by means of a simultaneous connection of the working chamber of an actuator to the low-pressure return and the high-pressure hydraulic accumulator be combined with a control or regulation of the delivery quantity by means of a hydraulic pump. While the above-mentioned connection of the working chamber can be used to exert very rapid and highly dynamic influence on the pressure in the high-pressure hydraulic accumulator, the control or regulation of the delivery quantity by means of the hydraulic pump permits a long-term, quantitatively substantial adaptation of the pressure in the high-pressure hydraulic accumulator.

[0020] The method according to the invention is particularly preferable if the actuator has two working chambers that are separated from each other by pressure surfaces on a piston, which are of different sizes and work in opposition to each other, and the one working chamber is continuously acted on by high pressure while the other working chamber can be connected to the high-pressure hydraulic accumulator and the low-pressure return. Actuators of this kind can achieve very short switching times, thus making it easier to execute the method according to the invention.

[0021] In order to prevent cavitation when the hydraulic fluid flows out of the working chamber into the low-pressure return, in the method according to the invention, the hydraulic fluid can also flow out of the working chamber into a low-pressure hydraulic accumulator. This reduces the pressure difference when the hydraulic fluid flows out, which counteracts cavitation.

[0022] The invention also relates to a computer program, which is suitable for executing the method according to one of the preceding claims when it is run on a computer. It is particularly preferable if the computer program is stored in a memory, in particular a flash memory or a ferrite RAM.

[0023] The invention also relates to a control and regulating unit for operating an internal combustion engine, which is connected at least to a first control valve and a second control valve of an electrohydraulic valve control, which can connect a working chamber of an actuator of a gas exchange device to a high-pressure hydraulic accumulator and/or to a low-pressure return.

[0024] In order to be able to simplify the electrohydraulic valve control, the invention proposes that the control and regulating unit be suitable for executing the above-mentioned method. It is particularly preferable if it is provided with a computer program of the type mentioned above.

DRAWINGS

[0025] A particularly preferred exemplary embodiment of the invention will be explained in detail below in conjunction with the accompanying drawings.

[0026]FIG. 1 schematically depicts an electrohydraulic valve control of an internal combustion engine;

[0027]FIG. 2 is a graph, which depicts the pressure curve over time in a high-pressure hydraulic accumulator from FIG. 1; and

[0028]FIG. 3 is a graph, which depicts the pressure in the high-pressure hydraulic accumulator from FIG. 1 over a speed of the internal combustion engine.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0029] In FIG. 1, an electrohydraulic valve control is labeled as a whole with the reference numeral 10. Firstly, it includes a reservoir for hydraulic fluid, which is labeled here with the reference numeral 12 and which can be the oil pan of the internal combustion engine. A controllable high-pressure hydraulic pump 14 feeds the hydraulic fluid from the hydraulic reservoir 12 into a high-pressure hydraulic accumulator 16. A hydraulic line 18 leads from the high-pressure hydraulic accumulator 16 to a solenoid valve 22 via a pressure control valve 20.

[0030] The hydraulic line 18 leads from the solenoid valve 22 to an actuator 24. This actuator is a hydraulic cylinder with a double-acting piston 26. The piston 26 is guided in a housing 28. Above the piston 26 in FIG. 1, a first working chamber 30 is formed between this piston and the housing 28. This working chamber 30 is connected to the solenoid valve 22. Below the piston 26 in FIG. 1, a second working chamber 32 is formed between this piston and the housing 28. This working chamber 32 is connected via a branch line 33 to the section of the hydraulic line 18 situated between the high-pressure hydraulic accumulator 16 and the solenoid valve 22.

[0031] In all, the end face 34 of the piston 26 at the top in FIG. 1 is larger than the end face 36 of the piston 26 at the bottom in FIG. 1, which end face 36 defines the second working chamber 32. The piston 26 is thus a so-called “differential piston”. The piston 26 is connected to a gas exchange valve 38, which has a valve rod 40 and a valve element 42. The valve element 42 can open or close an opening (no reference numeral) of a combustion chamber 44. The combustion chamber 44 is contained in an engine block 46 of an internal combustion engine (no reference numeral).

[0032] From the first working chamber 30 of the actuator 24, a hydraulic line 48 leads via a second solenoid valve 50 to a low-pressure hydraulic accumulator 52. This accumulator is in turn connected via a pressure control valve 54 to a low-pressure return 56, which finally leads back to the hydraulic reservoir 12. From the first working chamber 30 of the actuator 24, another hydraulic line 58 leads via a pressure control valve 60 back to the high-pressure hydraulic accumulator 16.

[0033] The two solenoid valves 22 and 50 are actuated by magnetic actuators 62 and 64 and are each pressed onto their neutral position by a compression spring 66 and 68. The first solenoid valve 22 is closed in its neutral position 70, in which the current to the magnetic actuator 62 is switched off, whereas it is open in the actuated switched position 72. By contrast, the second solenoid valve 50 is open in its neutral switched position 74 and is closed in the actuated switched position in which the magnetic actuator 64 is supplied with current. This actuated switched position is labeled with the reference numeral 76.

[0034] The electrohydraulic valve control 10 also has a control and regulating unit 78. On the output side, this unit is connected to the magnetic actuators 62 and 64. It can also control the hydraulic pump 14. On the input side, the control and regulating unit 78 is connected to a pressure sensor 80, which detects the pressure in the high-pressure hydraulic accumulator 16. The control and regulating unit 78 is also connected to a speed sensor for the crankshaft of the engine. This speed sensor is labeled with the reference numeral 82.

[0035] The electrohydraulic valve control 10 operates as follows (the method described hereinafter is stored as a computer program on a ferrite RAM (not shown) in the control and regulating unit 78): In order to open the gas exchange valve 38, the piston 26 must be moved downward in FIG. 1. This is achieved in that starting from the neutral position 74, the second solenoid valve 50 is supplied with current and is thus closed. This consequently breaks the connection between the first working chamber 30 and the low-pressure hydraulic accumulator 52.

[0036] Then the control and regulating unit 78 supplies current to the magnetic actuator 62 of the first solenoid valve 22 so that this solenoid valve 22 moves from its closed neutral position 70 into the open switched position 72. This connects the first working chamber 30 to the high-pressure hydraulic accumulator 16. Consequently, the hydraulic pressure prevailing in the high-pressure hydraulic accumulator 16 is also established in the first working chamber 30.

[0037] Since the lower end face 36 is smaller than the upper end face 34 of the piston 26, but the same pressure currently prevails in the two working chambers 30 and 32 of the actuator 24, namely essentially the pressure prevailing in the high-pressure hydraulic accumulator 16, this generates a resulting force in the downward direction in FIG. 1, thus causing the piston 26 to move in this direction as well. This also moves the valve rod 40 and the valve element 42 downward in FIG. 1, thus opening the gas exchange valve 38.

[0038] If the gas exchange valve 38 is to be closed again, then the control and regulating unit 78 initially switches off the current to the first solenoid valve 22 so that the compression spring 66 presses it from the open switched position 72 into the closed switched position 70. This consequently breaks the connection again between the high-pressure hydraulic accumulator 16 and the first working chamber 30.

[0039] Then the control and regulating unit 78 switches off the current to the second solenoid valve 50 so that the compression spring 68 moves it from the closed switched position 76 into the open neutral position 74. The first working chamber 30 is then reconnected with the low-pressure hydraulic accumulator 52. Consequently, the pressure in the first working chamber 30 decreases until a force resultant is produced, which moves the piston 26 back upward. This closes the gas exchange valve 38.

[0040] If the pressure sensor 80 notifies the control and regulating unit 78 that the pressure in the high-pressure hydraulic accumulator 16 is higher than a desired pressure, then the control and regulating unit 78 switches the first solenoid valve 22 into its open switched position 72 while the second solenoid valve 50 remains in its open neutral position 74. It is assumed here that the engine is in an operating state in which the gas exchange valve 38, which is connected to the actuator 24, should remain closed. Due to the above-mentioned actuation of the first solenoid valve 22, a direct connection has now been produced from the high-pressure hydraulic accumulator 16, via the first solenoid valve 22, the first working chamber 30, and the second solenoid valve 50, to the low-pressure hydraulic accumulator 52.

[0041] An appropriate layout of the hydraulic lines 18 and 48 can be used to achieve the fact that in this state, the pressure in the first working chamber 30 never gets high enough to induce an undesirable movement of the piston 26. The direct connection from the high-pressure hydraulic accumulator 16 to the low-pressure hydraulic accumulator 52 allows hydraulic fluid to flow from the high-pressure hydraulic accumulator 16 directly to the low-pressure hydraulic accumulator 52, without this resulting in a triggering of the actuator 24. This allows the pressure in the high-pressure hydraulic accumulator 16 to be deliberately reduced or kept constant.

[0042] If it is necessary to reliably prevent the gas exchange valve 38 from opening during this state, then the direct connection between the high-pressure hydraulic accumulator 16 and the low-pressure hydraulic accumulator 52 is preferably produced when a high pressure prevailing in the combustion chamber 44 presses the valve element 42 into its closed position.

[0043] The control and regulating unit 78 terminates the flow of hydraulic fluid out of the high-pressure hydraulic accumulator 16 into the low-pressure hydraulic accumulator 52 in a simple manner by switching the current to the first solenoid valve 22 off again so that it returns to its closed neutral position 70. The pressure prevailing in the low-pressure hydraulic accumulator 52 is then reestablished in the first working chamber 30.

[0044] The electrohydraulic valve control 10, however, can also be operated in a different manner in order to stabilize or reduce the pressure in the high-pressure hydraulic accumulator 16:

[0045] The connection of the high-pressure hydraulic accumulator 16 to the low-pressure hydraulic accumulator 52 can be coupled to a triggering of the actuator 24. When the actuator 24 is triggered so that the gas exchange valve 38 opens, for example just before the magnetic actuator 64 of the second solenoid valve 50 is supplied with current, which causes it to move from its open neutral position 74 into the closed switched position 76, the solenoid valve 22 can already have been moved from its closed neutral position 70 into the actuated and open switched position 72.

[0046] Consequently, shortly before the second solenoid valve 50 is closed, there is a direct connection between the high-pressure hydraulic accumulator 16 and the low-pressure hydraulic accumulator 52, which allows hydraulic fluid to flow out of the high-pressure hydraulic accumulator 16. In the same way, when the gas exchange valve 38 is to be closed again, just before the current to the magnetic actuator 62 of the first solenoid valve 22 is switched off, which causes this valve to move from its open switched position 72 back into the closed neutral position 70, the second solenoid valve 50 can already have been brought from its closed switched position 76 into the open neutral position 74.

[0047] This also produces a temporary direct connection from the high-pressure hydraulic accumulator 16, to the low-pressure hydraulic accumulator 52, and on to the low-pressure return 56, through which hydraulic fluid flows out of the high-pressure hydraulic accumulator 16, consequently allowing the pressure in this accumulator to be kept constant or to be reduced.

[0048] Such a temporary actuation of the valves and such a temporary connection of the high-pressure hydraulic accumulator 16 to the low-pressure return 56 permit the pressure in the high-pressure hydraulic accumulator 16 to be kept constant, as can be inferred from FIG. 2. The quantity of the fluid to be drained is controlled by the duration of the direct connection. In this figure, the pressure without a corresponding actuation of the solenoid valves 22 and 50 is depicted with a dashed line and the pressure curve that can be produced with a corresponding actuation of the solenoid valves 22 and 50 is depicted with a solid line.

[0049] When the engine is operated at a low speed, the engine speed sensor 82 detects this and sends a corresponding signal to the control and regulating unit 78. This unit can then trigger the solenoid valves 22 and 50 so that the pressure is reduced in the high-pressure hydraulic accumulator 16. Typically, the operating pressure of usually 200 bar is reduced to approximately 50 bar. If the speed increases again, then a direct fluid connection between the high-pressure hydraulic accumulator 16 and the low-pressure return is avoided so that the pressure increases again in the high-pressure hydraulic accumulator 16 due to the continuing supply by means of the high-pressure hydraulic pump 14. FIG. 3 depicts the relationship between the speed n of the engine and the pressure P in the high-pressure hydraulic accumulator 16. The pressure adjustment in the high-pressure hydraulic accumulator 16 can be assisted if need by through an appropriate triggering of the high-pressure hydraulic pump 14. 

1. A method for operating an electrohydraulic valve control (10) of an internal combustion engine, with at least one actuator (24) that acts on a gas exchange valve (38) and has at least one working chamber (30), which in order to switch the actuator (24) from a first position into a second position, is connected to a high-pressure hydraulic accumulator (16) and shut off from a low-pressure return (56), and in order to switch the actuator (24) from the second position back into the first position, is connected to the low-pressure return (56) and shut off from the high-pressure hydraulic accumulator (16), characterized in that the pressure in the high-pressure hydraulic accumulator (16) is kept constant or reduced by virtue of the working chamber (30) being connected to the high-pressure hydraulic accumulator (16) and the low-pressure return (56) at the same time.
 2. The method according to claim 1, characterized in that in order to stabilize or reduce the pressure in the high-pressure hydraulic accumulator (16), the working chamber (30) of an actuator (24) is connected to the high-pressure hydraulic accumulator (16) and the low-pressure return (56) simultaneously and its associated gas exchange valve (38) is closed at the time.
 3. The method according to claim 2, characterized in that in order to stabilize or reduce the pressure in the high-pressure hydraulic accumulator (16), the working chamber (30) of an actuator (24) is connected to the high-pressure hydraulic accumulator (16) and the low-pressure return (56) simultaneously and its associated gas exchange valve (38) cannot open at the time due to a high pressure in the combustion chamber (44).
 4. The method according to one of the preceding claims, characterized in that the working chamber (30) of an actuator (24), which is to be moved from the first position into the second position, is connected to the high-pressure hydraulic accumulator (16) just before being shut off from the low-pressure return (56), and/or the working chamber (30) of an actuator (24), which is to be moved from the second position into the first position, is connected to the low-pressure return (56) just before being shut off from the high-pressure hydraulic accumulator (16).
 5. The method according to one of the preceding claims, characterized in that the working chamber (30) of an actuator (24) is temporarily connected to the high-pressure hydraulic accumulator (16) and the low-pressure return (56) simultaneously when the internal combustion engine is operated at a low speed.
 6. The method according to one of the preceding claims, characterized in that there is also a control or regulation of the delivery quantity by means of the hydraulic pump (14).
 7. The method according to one of the preceding claims, characterized in that the actuator (24) has two working chambers (30, 32) that are separated from each other by pressure surfaces (34, 36) on a piston (26), which are of different sizes and work in opposition to each other, and the one working chamber (32) is continuously acted on by high pressure while the other working chamber (30) can be connected to the high-pressure hydraulic accumulator (16) and the low-pressure return (56).
 8. The method according to one of the preceding claims, characterized in that the hydraulic fluid flows out of the working chamber (30) into a low-pressure hydraulic accumulator (52).
 9. A computer program, characterized in that it is suitable for executing the method according to one of the preceding claims when it is run on a computer.
 10. The computer program according to claim 11, characterized in that it is stored in a memory, in particular a flash memory or a ferrite RAM.
 11. A control and regulating unit (78) for operating an internal combustion engine, which is connected to a first control valve (22) and a second control valve (50) of an electrohydraulic valve control (10), which can be used to connect a working chamber (30) of an actuator (24) of a gas exchange valve (38) to a high-pressure hydraulic accumulator (16) and a low-pressure return (56), characterized in that it is suitable for executing the method according to one of claims 1 to
 8. 12. The control and regulating unit (78) according to claim 12, characterized in that it is provided with a computer program according to one of claims 9 or
 10. 